This invention relates generally to printers, and more particularly to media ejection systems for stacking media sheets in an output region or output tray.
Print jobs commonly include multiple pages fed along a media handling system through a print zone into an output tray or output region. Pages are fed in series with one page along the media path at a time for some printers or with multiple pages along the media path at a time for other printers. Pages are stacked in the output tray. Many printers simply rely on gravity to stack the media sheets as the media sheets exit the media path. One solution has been to push new pages on top of previous pages resting in the output tray. Many laser printers, for example, use this method. A disadvantage of this technique is that pinch rollers often are needed to actively drive the current media sheet all the way along the previous sheet. For inkjet printers, this is undesirable because the previous sheet may still be wet. Star-wheels have been used in place of the pinch rollers, but the star wheels can leave tracks on the current media sheet.
The Hewlett-Packard DESKJET.RTM. Series printers include a movable pivot in the vicinity of the output tray and the inkjet pen cartridge. The pivot supports the media sheet beneath the inkjet pen as the media sheet passes through the print zone toward the printer's output region. Rail extensions (also referred to as wing devices) are included in the output region. As the media sheet passes from the print zone along the pivot into the output region, the leading edge is pushed onto rail extensions in the output region. The rail extensions receive the current media sheet and support the sheet above the previous media sheets in an underlying output tray. As the printing onto the media sheet completes, a sequence commences in which the pivot and rail extensions move down. The movement (or retraction) of the rail extensions causes the media sheet to fall into the output tray onto the previous media sheet. The movement of the pivot allows the trailing portion of the media sheet to slide from the pivot into the output tray under the force of gravity.
U.S. Pat. No. 5,226,743 issued Jul. 13, 1993 for "Method and Apparatus for Paper Control in a Printer," assigned to Hewlett-Packard Company discloses finger devices used during ejection. As printing onto the media sheet completes, a sequence commences in which a pivot rotates downward and wings retract. A pair of finger devices are pivotally attached to the underside of the pivot. The pivot includes openings for the finger devices. As the platen rotates down, the finger devices rotate up through the openings into contact with the trailing edge of the media sheet. As the media sheet falls from the wings and slides from the pivot, the finger devices give the media sheet a boost. Specifically, the finger devices urge the media sheet into the output tray onto any previous media sheets. Coordinating the movement of the finger devices and pivot adds complexity to the pivot design, requiring several parts (e.g., cam and spring and finger) for the actuation method.